Damaging herbicide drift can travel far

Every year, Eric Webster receives many calls on Newpath and Roundup drift. “The glyphosate drift is primarily in northeast Louisiana,” said the LSU AgCenter weed scientist at the recent field day at the Rice Research Station in Crowley, La. In southwest Louisiana, “we tend to see more Newpath drift — that’s due to the cropping culture and rice there is planted a bit earlier. We’re just now getting to the point where a lot of soybeans are being sprayed with glyphosate.”

In southwest Louisiana, glyphosate damage typically tends to show up more at harvest. “If Roundup drifted on the rice behind me,” said Webster pointing to a host of research plots, “it might be visible, or might not. But when the rice began heading out, it would be more obvious with blank heads.”

There have been two recent instances of Newpath drift in Acadia Parish. Both moved close to a mile from the target field. Webster sent samples of the rice foliage from one of the drift incidents to South Dakota State University for analysis.

“Along that mile stretch were several rice fields, and I could track the drift through them. The field closest to the Newpath target showed the lowest concentration (of the product). For reference, it showed a concentration of 2.2 parts per billion. The field farthest away showed the highest concentration at 8.8 parts per billion. So a mile away, the Newpath was four times higher than a field about 150 yards away from the (spray target).”

Webster said that points to an inversion layer. The morning the spray went out, the wind was 0 to 2 miles per hour coming from the east.

“Morning is often the worst time for a herbicide application. That’s when there tend to be more inversion layers. That morning, a cooler layer of temperatures was likely at the soil surface topped by a warmer air mass that’s moving across the field. The spray gets hung up and moves with the air mass.

“In some cases, the wind can even be moving in the opposite direction to the layer on the soil. That’s been documented in the state.”

Last year, LSU AgCenter researchers began studies “on Permit on the soil surface as a pre-emergence treatment. I’ve always put Permit in with Command blanket treatments to help with nutsedge control because it has residual activity.”

For the current test, “we left out the Command to see what Permit was bringing to the system. We found it was providing some broad-spectrum grass control — barnyardgrass, sprangletop and broadleaf signalgrass. We’ve since expanded that research and now have 10 or 12 studies.

“We haven’t seen the grass control we saw last year, although it is being suppressed. I think we’ll be able to put the product out early, expand the spectrum a bit and provide a bit longer residual.”

Webster is also looking at ammonium sulfate. “We’ve always known it helps with products like Roundup. This year, we’re checking it with Ricestar.

“We always want to find a grass herbicide that we can add a broadleaf herbicide to without causing any antagonism. Our research seems to show that products like Permit and Londax will accept 2 pounds of sprayable ammonium sulfate per acre. That’s along with the grass herbicides. We may be dropping the pH of the water and helping keep the products working independently.”